Preparation of glass containing selenium

ABSTRACT

Process for preparing a molten glass containing selenium as an additive material and an alkali metal oxide as one of the essential ingredients comprising the steps of mixing the source of selenium with a portion of a raw glass batch of which the content of the alkali metal oxide in percentage by weight is 1.510 times as large as that of the intended molten glass, sintering the resulting mixture at a temperature between 500* and 1,000* C., then mixing the sintered product and remaining portion of the raw glass batch, wherein the content of the alkali in the remaining portion of raw glass is reduced lower than that of the intended molten glass so as to balance the mean content of the alkali metal oxide in the above sintered product and the above remaining raw glass batch to that of the intended molten glass, and melting the latter mixture in a glass melting furnace.

United States Patent [72] lnventors Touru l'noue Nishinomiya-shi;Masakiyo Tachibnna, Takarazuka-shi, both of Japan [21] Appl. No. 788,966

[22] Filed Jan. 3, 1969 [45] Patented Dec. 21, 1971 [73] Assignee NipponSheet Glass Co., Ltd.

Higashi-ku, Osaka, Japan [32] Priority Jan. 10, 1968 [33] Japan [54]PREPARATION OF GLASS CONTAINING SELENIUM 5 Claims, No Drawings [52]U.S.Cl 65/18, 65/134, 106/52 [51] Int. Cl C031! 23/20 [50] FieldofSearch 65/17, 18,

[56] References Cited UNITED STATES PATENTS 2,892,726 6/1959 Smith106/52 3,29] ,585 12/1966 Okamura 65/18 Primary ExaminerS. Leon BashoreAssistant ExaminerRobert L. Lindsay, Jr. Attorney-Wenderoth, Lind &Ponack ABSTRACT: Process for preparing a molten glass containingselenium as an additive material and an alkali metal oxide as one of theessential ingredients comprising the steps of mixing the source ofselenium with a portion of a raw glass batch of which the content of thealkali metal oxide in percentage by weight is 1.5-l0 times as large asthat of the intended molten glass, sintering the resulting mixture at atemperature between 500 and l,000 C., then mixing the sintered productand remaining portion of the raw glass batch, wherein the content of thealkali in the remaining portion of raw glass is reduced lower than thatof the intended molten glass so as to balance the mean content of thealkali metal oxide in the above sintered product and the above remainingraw glass batch to that of the intended molten glass, and melting thelatter mixture in a glass melting furnace.

PREPARATION OF GLASS CONTAINING SELENIUM This invention relates to aprocess for compounding raw materials for glass including selenium. Towit, the invention relates to an improvement in the preparation of glasswhich contains selenium.

Selenium has been used for making glasses of various utilities, such asheat'absorbing glass and colored glass, or for decolorization of glass.According to the conventional practices, in most cases the selenium inthe form of metal or selenium compound is mixed and molten with othertotal amount of the raw materials for the glass. In such practices, theselenium tends to be volatilized during the melting step at hightemperatures. Thus in the ordinary flat glass composition, less thanonly percent of the added selenium remains in the product, the other 90percent or more having been lost during the melting. When the amount ofselenium to be added to glass batch mixture is increased in the purposeof increasing the selenium content in the glass, the loss ratio ofselenium is also increased. For this reason, an excessively large amountof selenium must be added to glass batch mixture, in order to obtain aglass colored deeply with selenium. Use of expensive selenium orselenium compounds in large amount not only results in high preparationcost but also makes the atmosphere in the vicinity of a glass-meltingfurnace toxic.

It has now been found that the loss of selenium during sintering ormelting of glass batch mixture is far less in the mixture containinggreater amount of a source of alkali metal oxide, compared with the caseof such mixture containing less alkali metal'oxide source.

Based on this discovery, the invention provides an improved process forthe preparation of selenium-containing molten glass by melting a glassbatch mixture of raw materials including a source of selenium, theimprovement residing in the steps of adding the source of selenium to aglass batch mixture of raw materials which leads to a glass compositionof higher alkali metal oxide content then that of the intended glasscomposition, sintering the resulting mixture, mixing the sinteredproduct with the balance of batch ingredients to form the intended glasscomposition, and melting the composition to provide the molten glass.

According to the present invention, the entire glass batch mixture ofraw materials (excluding the source of selenium) is divided into twoportions, and the selenium source is added to only one of the dividedportions. The portion mixed with the selenium source is sintered, andthen combined with the other portion of glass batch mixture, to betogether melted as the last step for making the intended molten glass.It is advantageous that the ratio of the portion mixed with the seleniumsource to the total of raw glass materials ranges approximatelyone-fiftieth to one-half, preferably one-thirtieth to onefifth. Also theportion to be mixed with the selenium source must be such a glass batchmixture as will form a glass composition of higher alkali metal oxidecontent then that of the intended glass composition.

Normally it is preferred that the glass batch mixture of raw materialsin which the selenium source is mixed should contain an alkali metaloxide source of the amount sufficient to lead the mixture to a glasscomposition containing an alkali metal oxide in an amount 1.5-) times aslarge as that of the alkali metal oxide in the intended glasscomposition. Again the preferred glass batch mixture is such that leadsto a glass composition of a network former content which is less thanthat of the intended glass composition, but is higher than approximatelyhalf of the network former content of the intended glass composition.Most common network former includes oxides of Si, B, and P, particularlySiO,.

The glass batch mixture mixed with a selenium source and which leads toa glass composition of higher alkali metal oxide content than that ofthe intended glass composition, is preferably shaped to a compressedform by pelletizing or briquetting prior to the sintering treatment.This compression is effective for reducing the voids among the particlesof raw materials, and consequently for improving the sintering result.

If desired, any suitable binder material such as sodium silicate, sodiumphosphate, sodium hydroxide or calcium hydroxide, etc., may be added tothe glass batch mixture.

The sintering temperature is variable according to the composition ofglass batch mixture to be sintered, but in most cases selected from therange of approximately 500-l,000 C. For normal flat glass composition,the sintering temperature can be selected from the range ofapproximately 700-l 000 C. When the glass batch mixture to be sinteredis compressed in advance, relatively low sintering temperatures can beemployed. Also the glass batch mixtures containing easily meltingcomponents such as NaOH NaC 1, LiCl, and Ca(OH),, can be sintered atstill lower temperatures. Thus, such easily meltable components may beadded to the glass batch mixtures in the purpose of making low sinteringtemperatures feasible.

Whereas, in one modification of the invention, the glass batch mixtureto which the selenium source is added is not only sintered, but alsomolten at approximately l,000 C. or at even higher temperatures. 1.

Thus sintered, or molten, glass batch mixture containing the seleniumsource is subsequently combined with the remaining portion of the batchingredients, and melted. It is preferred that the mixture is ground tohave the grain size almost the same as that of the remaining batchingredients, in advance of being combined with the remaining batchingredients.

The following examples are given strictly in the purpose of illustratingthe subject invention, but not for limiting the scope thereof. Thepercentages given in the examples are by weight.

EXAMPLE 1 This example illustrates the preparation of pink glass.

In order to obtain a glass composition as given in table I (which doesnot give the intended selenium content of the composition), the entireraw materials of the amounts given in the fourth column of table 2 wereeach divided into two portions of A and B, as indicated respectively insecond and third columns of table 2. The total amount of portion Acorresponds to approximately one-tenth of the entire raw materials.

Table l Intended Glass Composition When glass is produced from the glassbatch mixture of portions A above, glass of the composition as given intable 3 below is obtained. As can be understood upon comparing table 3with table 1, the Na,0 content of the glass composition led from theglass batch mixture of portions A is 29.0 percent, which is higher thanNa,0 content (13.5 percent) of the intended glass composition. Also theSiO content of the former is 57.6 percent, which is less than that (72.2percent) of the intended glass composition.

To the glass batch mixture of portions A, 1 kg. of metal selenium wasadded, and the resulting mixture was granulated into the pellets of -l2mm. b using a rolling drum pelletizer. The pellets were sintered atapproximately 800 C. for about 3 hours. Thus sintered product was groundto the particle size less than approximately 6 mesh (in accordance withJapanese Industrial Standard), and then mixed with the glass batchmixture of the raw materials of portions B. The resulting mixture wascharged in a glass-melting furnace to be melted. The obtained glass hasan absorption coefficient of 0.0657 mm. at a wavelength of 480 mu. Ingeneral, a glass containing selenium has an absorption bond atwavelengths ranging from 400 to 500 mp. and it exhibits a maximumabsorption at a wavelength of 480 mu. Therefore, the absorptioncoefficient at a wavelength of 480 m is referred to as the coloringdegree hereinafter.

b. The procedures of (a) above were repeated, except that 0.ll kg. ofmetal selenium was replaced by 0.05 kg. of metal selenium. The resultingflat glass was colored with the selenium, at the coloring degreeof0.0362 mm.".

c. For comparison, the entire raw materials of the glass as given in thefourth column of table 2 were not divided into two portions, and mixedwith 0.1 1 kg. of metal selenium. The resulting mixture was charged in aglass-melting furnace, melted, and formed into flat glass in the mannersimilar to that employed in (a). Thus obtained flat glass was coloredwith selenium, at the coloring degree of 0.03 66 mm.

From the foregoing, it can be understood that according to the subjectprocess, the coloring of flat glass with selenium can be achieved withthe effectiveness approximately l.8 times that of the case of using theequal amount of metal selenium in the conventional practice. lt can alsobe understood that the coloring of the same order as can be achieved byconventional practice is achievable with approximately half theconventionally used amount of metal selenium in accordance with thesubject process.

EXAMPLE 2 This example illustrates the preparation of gray glass.

in order to obtain a glass composition as indicated in table 5 (whichdoes not give the intended selenium content of the composition), thetotal raw materials of the amounts shown in fourth column of table 6were each divided into the portions A and B as respectively indicated insecond and third columns of table 6. The total amount of the portion Acorresponds to approximately one-twentieth of the entire raw materials.

Table 5 Intended Glass Composition Fe,0,, Oil

TiO 00] Total 99.66

Table 6 Ingredients (kg) Ingredient Portion A Portion B Total Siliceoussand 9.4 243.2 252.6

Dolomite 4.4 78.6 83.0

Sodium carbonate 8.8 69.4 78.2

Glaubers salt 2.9 2.9 Aplite l8.l 3.! Red iron oxide 0.48 0.48

Cobalt sulfate 0.08 0.08 Nickel oxide 0.05 0.05

Total 22.60 412.81 435.41

Table 7 Glass Composition Led from Mixture of Portions A sio, 54.3 A1,0, 0.7 F0 0; 0.06 Tio, 0.02 C 210 9.0 M g0 5 .0 M 0 30.4 Total 99.48

The glass batch mixture of portions A was mixed with 0| 1 kg. of metalselenium. Subjecting the mixture to the treatments similar to thosedescribed in the run (a) of example 1, molten glass was obtained. Withreference to the obtained glass, the total absorption coefficient andthose due to Fe O,, C00 and M0 at a wavelength of 480 mp. were measured.From these values, the absorption coefficient due to selenium alone wascalculated to be 0.0725 mmr'.

For comparison, the same raw materials of the same amount as specifiedin the above were mixed with 0.1] kg. of metal selenium, without havingbeen divided into the portions A and B. The resulting mixture wascharged in a glass-melting furnace, melted, and formed into flat glassin the similar manner. The coloring degree of the product with seleniumwas 0.0372 mmr What is claimed is:

1. In a method of preparing a molten glass containing selenium as anadditive material and an alkali metal oxide as one of the essentialingredients from a raw glass batch, the improvement which comprises thesteps of mixing a source of selenium selected from the group consistingof selenium and selenium compounds with one portion of a raw glass batchof which the content of the alkali metal oxide in percentage by weightis l .5-10 times as large as that of the finally desired molten glassproduct, sintering the resulting mixture at a temperature between 500and l,000 C, then mixing the sintered product with another portion ofthe raw glass batch having an alkali metal content lower than that ofthe finally produced molten glass so as to produce a glass of thedesired alkali metal oxide content, and melting the latter mixture in aglass-melting furnace.

2. The improvement according to claim 1, wherein the portion of the rawglass batch with which the source of selenium is to be mixed isapproximately one-fiftieth to one-half by weight of the total raw glassbatch.

3. The improvement according to claim 1, wherein the content of thenetwork former of the portion of the raw glass batch with which thesource of selenium is to be mixed is less than that of the finallyproduced molten glass and more than half of it.

4. The improvement according to claim 1, wherein the source of seleniumis metal selenium.

5. ln method of preparing a molten glass containing selenium as anadditive material and an alkali metal oxide as one of the essentialingredients, the improvement which comprises mixing a source of seleniumselected from the group consisting of selenium and selenium compoundswith a raw glass batch of which the content of the alkali metal oxide inpercentage by weight is 15-10 times as large as that of the finallydesired molten glass product, melting the resulting mixture at atemperature higher than l,000 C., then mixing the melted product withanother raw glass batch, wherein the content of the alkali metal oxideis lower than that of the finally desired molten glass product so as tobalance the mean content of the alkali metal oxide of the above sinteredproduct and the other raw glass batch to that of the finally producedmolten glass, and melting the latter mixture in a glass melting furnace.

I t i I III

2. The improvement according to claim 1, wherein the portion of the raw glass batch with which the source of selenium is to be mixed is approximately one-fiftieth to one-half by weight of the total raw glass batch.
 3. The improvement according to claim 1, wherein the content of the network former of the portion of the raw glass batch with which the source of selenium is to be mixed is less than that of the finally produced molten glass and more than half of it.
 4. The improvement according to claim 1, wherein the source of selenium is metal selenium.
 5. In method of preparing a molten glass containing selenium as an additive material and an alkali metal oxide as one of the essential ingredients, the improvement which comprises mixing a source of selenium selected from the group consisting of selenium and selenium compounds with a raw glass batch of which the content of the alkali metal oxide in percentage by weight is 1.5-10 times as large as that of the finally desired molten glass product, melting the resulting mixture at a temperature higher than 1,000* C., then mixing the melted product with another raw glass batch, wherein the content of the alkali metal oxide is lower than that of the finally desired molten glass product so as to balance the mean content of the alkali metal oxide of the above sintered product and the other raw glass batch to that of the finally produced molten glass, and melting the latter mixture in a glass melting furnace. 